This invention relates to paintable compositions. In one aspect, the invention relates to paintable compositions comprising polypropylene and at least one of (i) a substantially linear ethylene polymer, or (ii) an interpolymer of ethylene and an .alpha.,.beta.-unsaturated carbonyl. In another aspect, the invention relates to paintable compositions in which one or both of the polypropylene and substantially linear ethylene polymer are grafted with an unsaturated organic compound containing a carbonyl group, e.g. maleic anhydride. In yet another aspect, the invention relates to articles fabricated from these paintable compositions.
Thermoplastic polyolefins (TPOs) have many desirable properties, e.g. light weight, durability, low cost, etc., that make them an attractive material of construction for many consumer goods, e.g. interior and exterior automotive parts, decorative fascia for household appliances, and the like. However because of their nonpolar nature, TPOs do not readily accept paint or decorative print. Most paints and inks are polar in nature, and thus require a surface with some degree of polarity before it can adhere to the surface with any degree of desirable fastness.
In the past, this problem has been addressed from a number of different directions. One typical and effective method of applying a paint to a TPO is first to apply a primer to the TPO. Primer materials are typically compositions containing a halogenated polyolefin and an aromatic solvent and while widely recognized as effective, primers are expensive and their application is an extra step in the finishing of the TPO article.
Another effective approach is to subject the surface of a TPO article to a physical or chemical treatment, such as etching with a chemical abrasive or irradiating with a plasma. While generally effective, these methods are more complex in nature than the application of a primer, and thus more difficult to control in terms of quality and consistency from part to part.
Another approach is to modify the physical and/or chemical properties of the TPO either by blending it with other thermoplastic polymers, or by incorporating into it one or more polar groups, or both. For example, U.S. Pat. No. 4,946,896 to Mitsuno, et al. teaches a paintable TPO comprising 20-80 weight percent (wt %) polypropylene; 5-38 wt % of an ethylene copolymer consisting of ethylene, an ester unit of either alkyl acrylate or methacrylate, and an unsaturated dicarboxylic acid anhydride; and 5-70 wt % ethylene-propylene rubber. U.S. Pat. No. 4,888,391 to Domine, et al. teaches a paintable polyolefin composition comprising a blend of a polyolefin as the continuous phase with an ethylene/acrylate/acrylic acid terpolymer as the discontinuous phase. U.S. Pat. No. 4,945,005 to Aleckner, Jr., et al. teaches paintable TPOs comprising 2-25 wt % of a copolymer of an ethylenically unsaturated carboxylic acid and ethylene; 3-50 wt % of an ethylene .alpha.-olefin copolymer; optionally a crystalline homopolymer or copolymer of propylene; 5-50 wt % of an inorganic filler; and 10-35 wt % of a polyethylene or a copolymer of ethylene and an .alpha.-olefin. Co-pending U.S. Ser. No. 07/893,875 filed Jun. 5, 1992 teaches a paintable polyethylene comprising at least 50 wt % polyethylene grafted with at least about 0.01 wt %, based on the weight of the polyethylene, of an unsaturated organic compound containing at least one double bond and at least one functional acid group, e.g. maleic anhydride, and at least one thermoplastic polymer containing polar groups, e.g. polyurethane. Each of these disclosures are incorporated herein by reference.
While these and other modified TPO compositions all demonstrate some degree of efficacy, a continuing interest exists in identifying and developing new paintable TPOs.